In a printed circuit board for an electronic machine such as a computer, wiring is made of copper or the like in a prescribed pattern on at least one side of an electrically insulating base plate. The printed circuit board is manufactured as described from now on. A multi-layer film consisting of a photosensitive resin layer--which is a photoresist layer--and a light-transmissible resin film--which is a protective film for protecting the resin layer--is first bonded, under heat and pressure, to an electroconductive layer which is a thin copper film provided on the electrically insulating base plate. This heat and pressure bonding is performed in a mass production by a thin film bonding apparatus usually referred to as laminator. A wiring pattern film is then overlaid on the multi-layer film. The photosensitive resin layer is exposed to light through the wiring pattern film and the light-transmissible resin film for a prescribed time. The light-transmissible resin film is thereafter peeled from the photosensitive resin layer by a peeling unit. The photosensitive resin layer exposed to the light is then developed so that an etching mask pattern is created. After that, the unnecessary head of the electroconductive layer are removed by etching. The remaining portions of the photosensitive resin layer are then removed. The printed circuit board having wiring in the prescribed pattern is thus manufactured.
The multi-layer film consisting of the photosensitive resin layer and the light-transmissible resin film is bonded, under heat and pressure, to the electroconductive layer on the electrically insulating base plate by a conventional method of thin film bonding. Since the surface of the electroconductive layer has minute recesses and projections, air remains in the recesses when the multi-layer film is bonded to the surface of the electroconductive layer. For that reason, air bubbles are made between the mutually bonded surfaces of the multi-layer film and the electroconductive layer so that the adhesion of the film and the layer is lowered. This is a problem, and results in a reduced reliability of the wiring of the printed circuit board.
The present invention was made in order to solve the problem.
Accordingly, it is an object of the present invention to provide a method of bonding a thin film to a base plate so as to enhance the reliability of the assembly of the plate and the film stuck thereto.
It is another object of the present invention to provide a method for enhancing the reliability of printed circuit boards.
It is yet another object of the present invention to provide a method of preventing air bubbles from being made between the mutually bonded surfaces of a multi-layer film and an electroconductive layer provided on a base plate.
It is yet another object of the present invention to provide a method in which any excess air bubble preventive agent remaining on a pressure bonding roller and that remaining on a thin film bonded to a base plate are removed therefrom through suction, downstream of the roller in the direction of the conveyance of the base plate.
The above-mentioned and other objects of the present invention and the novel features thereof will be apparent from the description herein and the drawings attached hereto.